Compounds which absorb lights in a visible region develop various colors corresponding to the wavelength of the light absorbed. Such compounds are called dyes or dye stuffs and are used for coloring various materials, and as more higher usages, they are used as dyes for optical discs which are high density data-recording media, as spectral sensitizing dyes for silver halide photographic materials or electrophotographic materials which are image data-recording materials, or as filter dyes.
Dyes for use in these uses are in many cases dissolved in a solution in the first place and then processed to a desired state but as they are actually used in the state of amorphous, a solid state such as a solid dispersion, or an adsorption state, their property as molecular aggregate takes part in the performance of a product in which the are used. A minute molecular structural difference sometimes extremely affects the formation of molecular aggregate.
On the other hand, a spectral sensitizing technique is a very important and essential technique for producing a silver halide photographic material of high speed. With the development of a variety of spectral sensitizing dyes, the technical development in use of these sensitizing dyes such as supersensitizing techniques and addition methods has been done.
As spectral sensitizing dyes for use in spectral sensitization, it is known to use spectral sensitizing dyes, e.g., a cyanine dye, a merocyanine dye, a rhodacyanine dye, alone or in combination (e.g., in the case of supersensitization).
Sensitizing dyes for use for photographic materials should satisfy various conditions. That is, sensitizing dyes should be not only capable of achieving high spectral sensitivity but also should be less in fog, excellent in characteristics at exposure (e.g., latent image stability, reciprocity law characteristics, retention of temperature and humidity at exposure, etc.), less in the fluctuations of sensitivity, gradation and fog during storage of samples before exposure, and sensitizing dyes should not remain in a photographic material after development processing.
Of these conditions, high sensitivity is an essential condition and a great deal of effort has been expended, as disclosed, for example, in JP-A-60-202436 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-60-220339, JP-A-60-25147, JP-A-61-123834, JP-A-62-87953, JP-A-63-264743, JP-A-1-15534, JP-A-1-177533, JP-A-1-198743, JP-A-1-216342, JP-A-2-42, JP-B-60-57583 (the term "JP-B" as used herein means an "examined Japanese patent publication"), and U.S. Pat. No. 6,418,570.
However, some conventional compounds are insufficient in spectral sensitivity in a specific emulsion or in a specific wavelength region and have not reached satisfactory levels yet.
Further, with the realization of rapid development processing of a silver halide photographic material and the large addition amount of sensitizing dyes in recent years, a serious problem that sensitizing dyes contained in a silver halide photographic material do not thoroughly dissolve out during processing to color the photographic material (so-called residual color) has arisen.
Dyes having hydrophilic substituents, e.g., a sulfamoyl group and a carbamoyl group, at the nucleus have been investigated as sensitizing dyes which cause less residual color (e.g., JP-A-1-147451, JP-A-61-294429, JP-B-45-3249 and JP-A-61-77843), but these dyes have not reached sufficiently satisfactory level yet. The sensitizing dyes disclosed in U.S. Pat. No. 3,282,933 and EP-A-451816 have been certainly improved in residual colors but these dyes are also still not sufficient in the point of a compatibility of residual color with sensitivity.
The sensitivity of a silver halide photographic material is determined by the light absorption factor of a grain, the latent image-forming efficiency including the spectral sensitization efficiency and the minimum size of a latent image.
Of these factors, some well-known techniques with respect to the improvement of the light absorption factor of a grain will be described below. The techniques of high aspect ratio tabular grain emulsions disclosed in U.S. Pat. No. 5,494,789 etc. are techniques capable of increasing the adsorption amount of a dye per a grain as the surface area of a grain is increased, as a result capable of improving the light absorption factor. However, there is a limit in the method of increasing the surface area of a grain by making the aspect ratio of a grain higher, hence it becomes necessary to make the size of a grain larger for improving the light absorption factor of a grain.
In addition to the above, as methods of increasing the grain surface area of one grain, JP-A-58-106532 and JP-A-60-221320 disclose methods of making a pore at one part of a grain, and U.S. Pat. No. 4,643,966 discloses a ruffled grain. However, the forms of these grains are unstable arid can be put to practical use with extreme difficulty.
Further, U.S. Pat. No. 5,302,499 discloses that a light absorption factor of a grain can be improved by the layer constitution having spectral sensitization characteristics and an optimal grain thickness. However, the increase of a light absorption factor by the optimization of a grain thickness is at most 10% or so.
Accordingly, it is necessary to increase the light absorption factor of the unit surface area of a grain for remarkably increasing the light absorption factor per one grain while maintaining the grain size small in a stable state. It becomes necessary to heighten the adsorption density of a sensitizing dye for that purpose, but generally used spectral sensitizing dyes are adsorbed onto the monomolecular layer at almost the closest packing density and cannot be adsorbed beyond that.
Some techniques have been suggested for solving this problem. For example, P. B. Gilman, Jr., et al. made a cationic dye adsorb onto the first layer and further an anionic dye onto the second layer as described in Photographic Science and Engineering, Vol. 20, No. 3, p. 97 (1976).
G. B. Bird, et al. made a plurality of dyes adsorb onto silver halide by multilayer adsorption and effected sensitization due to Forster type excitation energy transfer as disclosed in U.S. Pat. No. 3,622,316.
Sugimoto et al. performed spectral sensitization due to energy transfer from a luminescent dye in JP-A-63-138341 and JP-A-64-84244.
R. Steiger et al. tried spectral sensitization due Lo energy transfer from a gelatin-substituted cyanine dye in Photographic Science and Engineering, Vol. 27, No. 2, p. 59 (1983).
Ikekawa et al. conducted spectral sensitization due to energy transfer from a cyclodextrin-substituted dye in JP-A-61-251842.
These are all trials to intend to make a dye of the amount more than a saturation adsorption amount adsorb onto a silver halide grain, but any of these is not so effective to improve sensitivity. On the contrary, there are problems of the increase of intrinsic desensitization and development inhibition in these patents.
On the other hand, two-component connected dyes comprising two or more non-conjugated chromophores of dyes connected by covalent bonding are disclosed in U.S. Pat. Nos. 2,393,351, 2,425,772, 2,518,732, 2,521,944, 2,592,196 and European Pat. No. 565083. However, the objects of these patents were not to intend to increase a light absorption factor. As techniques which positively aimed at improving a light absorption factor, G. B. Bird and A. L. Borror contrived sensitization by the contribution of energy transfer by the adsorption of connection type sensitizing dye molecules having a plurality of cyanine chromophores to thereby increase a light absorption factor, as disclosed in U.S. Pat. Nos. 3,622,317 and 3,976,493. Borror describes with respect to sensitizing dye compounds having two chromophores connected by an alkylene-amide moiety. These compounds are produced by condensing a first dye with the quaternary salt of a second dye, then reacting a new quaternary salt with ICI intermediate by an ordinary dye-forming reaction. According to this procedure, two-component connected dyes can be obtained in high yield but sometimes impurities are generated, and these impurities cause desensitization even with an extremely low concentration. In conclusion, the present situation is that sufficient sensitivity improvement cannot be obtained from these techniques.
Ukai, Okazaki and Sugimoto suggest in JP-A-64-91134 to bond at least one substantially non-adsorptive dye containing at least two sulfo group and/or carboxyl group to a spectral sensitizing dye which is adsorbable onto silver halide.
Ral Chand Bishwakalma and Thomas Robert Dobles performed spectral sensitization by using two-component connected dyes comprising connecting cyanine adsorptive onto silver halide and non-adsorptive oxonol as disclosed in JP-A-6-27578, but it cannot be said that sufficient improvement of sensitization by the contribution of energy transfer has been attained.
Thus any method of the above patents and literature is insufficient with respect to the light absorption factor per a unit area of silver halide grain and further technical development is required.
Not many a methine compound having a heterocyclic condensed ring type and benzene condensed ring type basic nucleus has been known until now. For example, a cyanine dye having indole[2,3-f]benzothiazole as a nucleus and a cyanine dye having benzothieno[2,3-f]benzothiazole as a nucleus described in Zu Nauchn Prikl Fotogr., 1997, 42 (6), 27, a cyanine dye having methylenedioxy-substituted benzothiazole described in JP-A-2-272443, an oxyindole condensed ring type oxazole derivative disclosed in European Patent 334289, a tetrahydrodioxoquinazoline condensed ring type thiazole derivative described in Chem. Pharm. Bull., 1986, 34 (3), 1384, and cyanine dyes having a coumarine condensed ring type thiazole derivative and a dihydrooxobenzo condensed ring type thiazole as a nucleus described in Curr. Sci. 1984, 53 (8), 424 are known. Cyanine dyes derived from benzofuro[2,3-f]benzoxazole are disclosed in British Patent 1,168,495, but indole[3,2-f]benzoxazole, benzothieno[f]benzoxazole, benzofuro[3,2-f]benzoxazole, etc., having different condensed ring forms are not known.